Voltage reference circuit with breakpoint compensation

Abstract

A voltage reference circuit includes a band-gap reference circuit for providing a reference voltage and having breakpoint compensation to adjust the temperature coefficient of the reference voltage as a function of temperature. A thermal limit transistor biased by a voltage having a positive temperature coefficient begins conducting when the operating temperature reaches a predetermined value to provide a compensation current. The compensation current is added to the collector current flowing into one of a pair of transistors within the band-gap reference circuit, and a current controlled current source responds to an increase in collector current in the other one of the pair of transistors by making the collector currents flowing into both transistors equal. This increases the voltage drop across a pair of resistors to increase a band-gap voltage across a portion of an output divider network, to in turn increase the reference voltage provided across the entire divider network.

We claim: 
     
       1. A voltage reference circuit comprising: a band-gap reference circuit having a plurality of transistors and operative to produce a reference voltage in accordance with the amount of conduction of the plurality of transistors;   means for generating a compensating current in accordance with operating temperature of the voltage reference circuit; and   means for applying the compensating current to the band-gap reference circuit to vary the amount of conduction of the plurality of transistors in accordance therewith;   each of the plurality of transistors having a collector current flowing therein, and the means for applying the compensating current adding the compensating current to the collector current flowing in one of the plurality of transistors.   
     
     
       2. A voltage reference circuit comprising: a pair of transistors having collector, base and emitter terminals, the base terminals being coupled together;   means coupled to the collector terminals of the pair of transistors for providing a pair of currents thereto;   means for attempting to maintain the pair of currents approximately equal;   a plurality of resistors coupled to the pair of transistors to provide a reference voltage; and   means for providing a compensation current in accordance with operating temperature of the voltage reference circuit, the compensation current being applied to the collector terminal of one of the pair of transistors.   
     
     
       3. The invention set forth in claim 2, wherein the means for providing a compensation current comprises a transistor coupled to be biased by the serial combination of a constant voltage source and a resistor. 
     
     
       4. The invention set forth in claim 2, wherein the means for providing a compensation current is operative to begin providing the compensation current when the operating temperature reaches a predetermined value and to increase the compensation current in response to increasing operating temperatures above the predetermined value. 
     
     
       5. The invention set forth in claim 2, wherein the means for attempting to maintain the pair of currents approximately equal comprises a second pair of transistors having base terminals coupled together and each having a conductive path coupled between a voltage source via a different one of a pair of resistors and a difference one of the first-mentioned pair of transistors, the base terminal of one of the second pair of transistors being coupled to the conductive path thereof. 
     
     
       6. The invention set forth in claim 2, wherein the plurality of resistors comprises a first resistor coupled between the emitter terminals of the pair of transistors, a voltage divider network coupled to the base terminals of the pair of transistors, and a second resistor coupled between the emitter terminal of one of the pair of transistors and the voltage divider network. 
     
     
       7. A voltage reference circuit comprising: a plurality of transistors, each having emitter, base and collector terminals and a source current flowing thereto from a current source;   means for maintaining the source currents flowing to each of the plurality of transistors approximately equal;   resistor means coupled to the plurality of transistors for providing a reference voltage in accordance with conduction of the plurality of transistors; and   means coupled to the collector terminal of one of the plurality of transistors for providing to the collector terminal a temperature compensation current in accordance with temperature.   
     
     
       8. The invention set forth in claim 7, wherein the resistor means is coupled to the emitter terminals and to the base terminals of each of the plurality of transistors. 
     
     
       9. The invention set forth in claim 8, wherein the plurality of transistors comprises first and second transistors and the resistor means comprises a first resistor coupled between the emitter terminals of the first and second transistors, a voltage divider network coupled to the base terminals of the first and second transistors, and a second resistor coupled between the emitter terminal of the first transistor and the voltage divider network. 
     
     
       10. The invention set forth in claim 9, wherein the voltage divider network comprises first and second output terminals for providing a reference voltage, a third resistor coupled between the first output terminal and the base terminals of the first and second transistors, and a fourth resistor coupled between the second output terminal and the base terminals of the first and second transistors, the second output terminal also being coupled to a side of the second resistor opposite the emitter terminal of the first transistor. 
     
     
       11. The invention set forth in claim 10 wherein the means for providing a temperature compensation current comprises a thermal limit transistor having emitter, base and collector terminals, the collector terminal being coupled to the collector terminal of the first transistor, a resistor coupled to the emitter terminal and a constant voltage source coupled between the base terminal and the resistor.